1. Field of the Invention
The present invention relates to a power supply control circuit and a control method thereof, and, in particular, to a power supply control circuit provided in a board-type module in a hot plug type, and a control method thereof.
2. Description of the Related Art
For example, in an optical communication apparatus or such in which many optical modules are inserted, replacement or such of the respective optical modules is carried out in a hot plug state since the optical communication apparatus operates continuously in terms of its function.
In such a hot plug optical module insertion/removal, a power supply electric current (simply referred to as ‘a power supply current’, hereinafter) is supplied to the optical module simultaneously upon insertion of the optical module to the optical communication apparatus body for the purpose of starting up the optical module. However, in such a case, a large rush current may flow in relation to circuit impedance concerning the optical module. Thereby, a large voltage drop occurs in the optical communication apparatus accordingly, which may exert influence on operation of other modules in the apparatus.
That is, when a power supply fluctuation occurs due to the above-mentioned voltage drop, stable operation of the other modules in the apparatus may not be ensured. In order to avoid such a situation, it is necessary to control a rush current occurring upon insertion of the optical module, within a predetermined limit.
In such a communication apparatus, a capacitor may be inserted in a power supply line for the purpose of avoiding introduction of power source noise. However, when the capacitor for avoiding power source noise having a large capacitance is inserted for the purpose of improving the power source noise elimination effect, the rush current occurring upon the above-mentioned module hot plug insertion tends to increase. Therefore, it is necessary to improve the power source noise elimination effect with controlling the capacitance of the power source noise elimination capacitor in a low level.
In order to solve this problem, a control of flowing an electric current in such a direction as to cancel the rush current by means of feed-forward control, a control of reducing a resistance of a resister at a certain reduction rate, and so forth have been proposed.
However, such methods involve problems that a time required for starting up the optical module upon insertion thereof becomes longer, a large variation occurs in the rush current actually occurring upon hot plug insertion in relation to circuit operation in the load circuit, and so forth.
Japanese Laid-open Patent Applications Nos. 07-143736, 08-30341, 63-200614 and 07-302142 disclose the related arts.